Dynamic metrology schemes and sampling schemes for advanced process control in semiconductor processing

ABSTRACT

Systems, methods and mediums are provided for dynamic adjustment of sampling plans in connection with a wafer (or other device) to be measured. The invention adjusts the frequency and/or spatial resolution of measurements on an as-needed basis when one or more events occur that are likely to indicate an internal or external change affecting the manufacturing process or results. The dynamic metrology plan adjusts the spatial resolution of sampling within-wafer by adding, subtracting or replacing candidate points from the sampling plan, in response to certain events which suggest that additional or different measurements of the wafer may be desirable. Further, the invention may be used in connection with adjusting the frequency of wafer-to-wafer measurements.

RELATED APPLICATION

This application is a divisional of U.S. patent application Ser. No.10/135,451, filed May 1, 2002, which claims the benefit of U.S.Provisional Application Ser. No. 60/322,459, filed Sep. 17, 2001, whichis expressly incorporated herein by reference; and U.S. ProvisionalApplication Ser. No. 60/298,878, filed Jun. 19, 2001, which is expresslyincorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention concerns computer-related and/or assisted methods,systems and computer readable mediums for metrology during processcontrol. More specifically, it relates to dynamic adjustment ofmetrology schemes and sampling during advanced process control methods,for example during control of semiconductor technology manufacture.

2. Related Art

In the wafer fabrication art, measurements are made by metrology toolson wafers as they are being manufactured by processing devices, in orderto ensure that the wafers are produced according to a predefinedspecification. The measurements are made of physical properties such asfilm thickness and uniformity, dopant concentration, gate length andcritical dimension. This is known as the science of “metrology.”

Measurements to be made are typically specified in a “die map”. The diemap indicates where the different chips (or die) are located on a wafer(in the typical situation where multiple chips are formed on andeventually cut from a single wafer), as well as significant locations,such as corners, on each die. In order to measure the right hand corneron each die, for example, multiple points are measured on the wafer inaccordance with the die map. Ordinarily a die map is a digitalrepresentation of coordinate points, or “metrology coordinates,” on thewafer.

The metrology coordinates are usually provided by an engineer, and varydepending on the engineer's preferences. Metrology coordinates areconventionally provided as x, y coordinates.

A “sampling plan,” alternatively referred to as a “metrology plan,”contains metrology coordinates drawn from the die map. The sampling plandenotes a specific plan for taking certain measurements. Thesemeasurements may include some or all of the possible points and/or chipsin the die map.

A conventional metrology system assigns a sampling plan thatpredetermines which wafers are to be measured in connection with aprocessing device, and the measurements which are to be taken of thosewafers by the metrology tool. For example, the sampling plan mightdefine that each fifth wafer should be measured at pre-designatedlocations. These sampling plans are not changed after being initiallyassigned, and hence the metrology systems are static.

Unfortunately, manufacturing results tend to drift away from theintended target or specification when there is a change in themanufacturing process, such as a change in recipe, preventativemaintenance, consumables change, environmental change or a new lot ofwafers. Conventional metrology systems tend to miss some wafers whichare outside specification limits, since these systems use a virtuallyconsistent measurement scheme, having consistently frequent measurementswith consistent spatial resolution, without taking into considerationwhether any changes were introduced into the manufacturing process whichmight change the manufacturing results.

Manufacturing systems do not typically call for a measurement of everywafer, since measuring takes time and increasing the number ofmeasurements results in a decrease of productivity. On the other hand,measuring fewer wafers tends to lead to delayed detection of criticalinformation for process control that may significantly impact waferyield. While conventional sampling systems will sample wafers duringand/or after production, these systems do not adjust the initiallyassigned sampling plan for the wafers during production.

Thus, there remains a need for dynamic metrology to improve the qualityof products. For semiconductor wafers, there remains a need to bettercheck whether each specification is met under production conditions.There also remains a need to respond to a change in parameters which maycause a variance from intended target results, such as recipeparameters, and to adjust the frequency and/or spatial resolution ofmeasurements. Unfortunately, taking measurements takes time, and mostprocessing devices are faster than the measurements that need to betaken by metrology tools in order to characterize the wafers using ametrology. Thus, there remains a need for a method, system and medium toreact to changes potentially affecting the system results, and toappropriately adjust, increase, or decrease the measurementsaccordingly.

SUMMARY OF THE INVENTION

The present invention alleviates the problems of the conventionaltechniques described above by dynamically determining whether a waferneeds to be measured for process control based on changes in theresources, recipes, etc. In addition, for a given wafer to be measured,measuring points are also dynamically assigned to the metrology tool.

More specifically, two variations of embodiments of the presentinvention are contemplated and may be used independently or together.According to the first variation, the frequency at which wafers aremeasured (“wafer-to-wafer”) is adjusted, following an event thatsuggests that more (or fewer) wafers should be measured. According tothe second variation, the spatial resolution of the measurements ofthose wafers selected for measurement (“within-wafer”) is increased ordecreased, following an event that suggests each wafer which is measuredshould be measured in greater (or lesser) detail.

In one or more embodiments of the present invention, candidatecoordinate measurement points are mapped in a die map, and a subset ofthe candidate coordinate measurement points are selected as the initialpoints where measurements are to be made. Subsequently, according to thewithin-wafer variation, the invention dynamically selects more, fewer ordifferent points (depending on the circumstances) to be measured fromamong the candidate coordinate measurement points. According to thewafer-to-wafer variation, when there is a change in the manufacturingprocess, the number of measurements may be increased, to measure everywafer rather than just every third wafer for example. As one example,when a new recipe is implemented to significantly change the thicknessat a particular region on the wafer, a greater number of within-wafermeasurements can be made at that location by selecting more and/ordifferent candidate measurement points. As another example, when a faultis detected, the frequency of wafers selected for measurement isincreased; this increases the probability of detecting defectivelymanufactured wafers and correcting the control parameters (such as inconnection with a feed forward/feedback method). In some situations,large deviations may require less frequent measurement or less spatialresolution than small deviations when the large deviations clearlyidentify the problem, whereas small deviations may be difficult toidentify and more frequent and/or dense measurements may be necessary.The reverse may be appropriate in other situations regarding thefrequency and density of measurements, or it may be the case that thesame number of measurements may be taken regardless of deviation.

According to one or more embodiments of the present invention, there isprovided a method, system and/or computer-implemented method formeasuring at least one manufacturing characteristic for at least oneproduct manufactured by a manufacturing process. Information isprovided, representative of a set of candidate points to be measured bythe manufacturing process on the at least one product. The manufacturingprocess executes a plan for performing measurements on the at least oneproduct to measure the at least one manufacturing characteristic, theplan defining the measurements to be made responsive to the set ofcandidate points. A change in the manufacturing process is detected, thechange including at least one of: receiving new material in themanufacturing process, detecting a fault in the manufacturing process,detecting a change in a control parameter in the manufacturing process,and detecting a variation in a measurement of the at least one product.

According to one or more embodiments, the plan for performingmeasurements is adjusted on the detected change and at least oneadditional measurement is performed responsive thereto.

According to one or more embodiments, the measurements of the plan areadjusted wafer-to-wafer and/or within-wafer.

According to one or more embodiments, the product is a semi-conductorwafer and the manufacturing process is an automated semi-conductormanufacturing process.

According to one or more embodiments, the plan further includesinformation representative of a metrology recipe.

According to one or more embodiments, the candidate points are includedin a map corresponding to the at least one product. The plan may be apre-determined sampling plan.

According to one or more embodiments, the plan defines at least oneregion on each of the candidate points corresponding to the at least oneregion.

According to one or more embodiments, the adjustment includesdetermining the at least one region corresponding to the detectedchange, selecting the at least one additional measurement responsive tothe candidate points corresponding to the determined region, assigningthe selected at least one additional measurement to be performed underthe plan, and revising at least one of the measurements, the additionalmeasurement and the plan. The adjustment may include determining whetherthe detected change may affect a series of products, and if so,determining whether to measure at least one of the products in theseries of products. The products may be provided in a group, and theplan may further include first information representative of theproducts in the group that are available to be measured, and secondinformation representative of the products in the group that are to bemeasured under the plan.

According to one or more embodiments, information representative ofmeasurement results on the product is discarded when the measurementsresults indicate a variation in measurement of the product and/or when afault is detected in the manufacturing process.

According to one or more embodiments, the sampling plan includes aplurality of splines radiating from a center of a product, and thecandidate points are distributed along the splines. The distribution ofthe candidate points along the splines may be weighted according to asurface area of the product. According to one or more other embodiments,the sampling plan includes a plurality of radially distributed candidatepoints.

BRIEF DESCRIPTION OF THE FIGURES

The above mentioned and other advantages and features of the presentinvention will become more readily apparent from the following detaileddescription in the accompanying drawing, in which:

FIG. 1 is a flow chart showing one example of dynamic metrology for“wafer-to-wafer” processing in the present invention.

FIGS. 2A and 2B are an illustration of regions on a wafer, with FIG. 2Abeing a plan view of the wafer and FIG. 2B being a cross-section of thewafer along radius B-B of FIG. 2A.

FIG. 3 is a flow chart showing one example of dynamic metrology for“within-wafer” processing in accordance with one or more embodiments ofthe present invention.

FIGS. 4A and 4B are a spiral sampling plan for a wafer for use with oneor more embodiments of the invention, with FIG. 4A being a plan view ofthe wafer and FIG. 4B being a cross-section of the wafer along a radiusof FIG. 4A.

FIG. 5 is an example of another sampling plan for use with one or moreembodiments of the invention.

FIG. 6 is a block diagram of a computerized process control system whichmay be used in connection with one or more embodiments of the presentinvention.

DETAILED DESCRIPTION

The following detailed description includes many specific details. Theinclusion of such details is for the purpose of illustration only andshould not be understood to limit the invention. Throughout thisdiscussion, similar elements are referred to by similar numbers in thevarious figures for ease of reference. In addition, features in oneembodiment may be combined with features in other embodiments of theinvention.

In one or more embodiments of the present invention, static metrologymeans there is a pre-determined sampling plan in connection with a wafer(or other device) to be measured, specifying substantially the samepoints for each wafer (or the other device). In contrast, a dynamicmetrology plan utilizes an initial sampling plan and adjusts thesampling responsive to certain events or non-events. As an example of anadjustment due to a non-event, if the last ten wafers measured are allthe same, and if the processing device did not change, and if the recipeon the processing device did not change, one could reasonably assumethat the next series of wafers will have measurements that are also allthe same. That being the case, then in order to increase throughput anddecrease the time it takes to do measurements, the invention providesfor dynamically adjusting the measurements, for example, such that everythird wafer instead of every wafer is measured. This invention thusdetects and adjusts for not only potential errors, which could arise forexample upon a recipe change, but also for accuracy.

One or more embodiments of the present invention contemplate that theinvention may be used in connection with wafer-to-wafer measurementsdescribed above, as well as, or alternatively, in connection withwithin-wafer measurements. Consider an example of within-wafermeasurements, in which measurements are taken along a radius of a 200 mmdiameter wafer and the radius is measured in 10 mm increments. Duringprocessing it is noted or detected by the usual detection process thatthere is a large variation at the 50 mm and 60 mm points. For the nextsample, the system adjusts to measure another point from the samplingplan between 50 mm and 60 mm to better characterize that variation, oroptionally to measure an additional point, for example, between 40 mmand 50 mm that is near the location of the variation. If the die mapincludes points at 45 mm and 55 mm, these points can then be added asmeasurement points. Adjusted measurements now encompass in this example,40 mm, 45 mm, 50 mm, 55 mm, and 60 mm. The system dynamically added thetwo additional points (in the example) to better characterize themeasurement and/or the variation. Where there are provided a number ofcandidate points in the die map allowing points to be added orsubstituted, the system can select among the points any of several ways,such as selecting the closest to mean, mode, other statistical analysis,etc.

A sampling plan provides specific measure points within a die, a diebeing the section on the wafer that will typically eventually become asingle chip after processing. There are specified points within the diethat are candidates for measuring. The map of the die is stored,preferably in an electronic format representing the map. One appropriateplace for storing the die map information is in the factory automationsystem (“MES” or manufacturing execution system). The stored die mapinformation may be advantageously retrieved and translated to determinethe available points for measurement on the wafer. Referring back to theprevious example proposing measurement points on the radius at 45 mm and55 mm, if these specific points are not relevant to the current die(e.g., they are not specified by the die map), an appropriatereplacement would be points selected from the candidate points specifiedby the die map which are close to or between 45 mm and 55 mm. Thosepoints could be selected dynamically as well. Other criteria may be usedfor selecting points as well.

Dynamic metrology is performed to better meet a certain specification.For example, if recipe parameters are changed on the processing device,to adjust the thickness of a film that is deposited on the wafer, it maybe desirable to more closely check whether the specification is stillbeing achieved by performing measurements.

In order to avoid slowing down the process, one or more embodiments ofthe present invention advantageously determine the appropriateness ofperforming additional measurements when one or more events occur thatare likely to indicate an internal or external change affecting themanufacturing process or results. The increase in measurements andpossible corresponding decrease in processing occur on an as-neededbasis and/or based on predetermined criteria.

The wafer-to-wafer variation of the invention, for example, can checkfor events which may affect a series of wafers and may adjust thesampling plan. For example, during processing, the system determines ifan increase is needed in the frequency of wafers measured for processcontrol, for example, based on—1) a change in the processing device thewafers are processed on, 2) a change in the parameters or recipe thatwere used by the processing device to process the wafer, 3) largedetected variations or errors in measurements, and/or 4) a significantrun of wafers without errors.

Particularly regarding within-wafer variation, one or more embodimentsof the present invention contemplate that the system obtains a storeddie map with metrology coordinate information from the MES. Asindicated, the system can provide not only for assigning the measurementpoints optionally dynamically, but also for de-assigning.

One or more embodiments of the present invention envision changing thesampling plan using information that is gathered from the MES andautomatically using that new sampling plan, depending on, for examplethe type of processing device on which the wafers are processed.Advantageously, the system has stored information about a wafer thatindicates, among other things, the type of chip or type of device and anassociated sampling plan to be used when measuring a wafer containing aspecific device. Based on the type of device, the associated samplingplan or die map can be obtained, where the die map includes a set ofcandidate metrology points. The system then selects metrology points forthe current wafer from the set of, or responsive to, the candidatepoints in the die map.

With respect to the sampling plan, generation of the sampling plan canvary from device to device (chip type to chip type) and somemeasurements may be based on die distribution on the wafer. By dividinga wafer into regions and using regions of the wafer for measurement, oneor more embodiments of the present invention provide flexibility inselecting one or more points from available points in the region. Use ofregions is one way to provide a pool of candidate points, from which thesystem may select points that are most relevant to the desiredinformation about the film on the wafer.

In practice, the system may, for example, measure twenty-two totwenty-five points per wafer from the pool of candidate points. For someprocesses the system might measure fewer points, such as eight points,because it takes longer to measure those points or the wafer—processingtime—is faster. For other processes the system might measure one pointof another type of property, such dopant concentration, which is arelatively slow measurement.

In any event, it is important to balance the time consumed in ameasurement against the need to produce quality products. Manufacturersconsider it to be more important to be within specifications and notproduce defective product, than to rapidly produce product of suspectqualities.

Each processing device on which a wafer is processed has a differentprocessing time, and therefore the selected standard sampling rate maydepend on the speed of processing of the processing device and metrologytool. On some processing devices, measurements on every wafer will notslow down processing since the speed of the processing device is slowerthan the measurements by the metrology tool. For example, polishing andcleaning processing devices may consume five minutes or more to processa wafer. In that case a post-processing measurement by the metrologytool on every wafer would often not reduce throughput.

Additionally, the system may determine whether or not to make additionalmeasurements based on the initial and the final condition of the wafers.For example, if there is a situation in which the incoming thicknessprofile of a cross section of a wafer does not change very much, thesystem may reduce the frequency of samples of incoming profiles,wafer-to-wafer. On the other hand, if the incoming profile is changingsignificantly, it may be desirable to measure every entering wafer.

Reference is made to FIG. 1, illustrating an example of a flow chart forone or more embodiments of a wafer-to-wafer dynamic metrology system.The system checks whether there may have been a significant change inthe state of the processing device, which can be detected by checking,for example, idle time, change of consumables, etc. There may be otherevents that could be checked that would indicate a potential change inthe processing device or lead one to believe that it might have beenchanged. It is possible that the processing device itself may includesufficient programming to recognize or track those type of events. Theflowchart example in FIG. 1 includes an example set of events or statechanges that initiate analysis and decision-making, based uponinformation gathered from the processing device and based on asignificant internal or external change (e.g., system was idle for along time, chamber was cleaned, new batch of slurry, initial wafer,etc.). Other events or states may be included in the set from which itis determined whether or not to measure a wafer.

One or more embodiments, of the present invention also envision thefollowing. Assume that there is provided an initial sampling plan. Theplan could, for example, direct measuring of specific points on eachwafer and/or comprise information indicating which wafers within the lotwill be measured. The wafer is measured according to the sampling plan.According to the wafer-to-wafer metrology plan, the system deviates fromthe initial sampling plan when warranted. The system could return to theinitial sampling plan once it detects that the process is again “normal”or again producing product within specification.

Referring still to FIG. 1, consider for example a typical cassette oftwenty-five wafers to be processed according to one or more embodimentsof the present invention. The cassette of wafers arrives at theprocessing device, usually from some other processing device, andprocessing on the lot is started, at block 101.

If a wafer being processed by a processing device is the first wafer ofa particular lot on the processing device then it may be desirable tomeasure this wafer, in order to detect if perhaps there was someprocessing device related property that changed. Thus, at block 103, thesystem checks whether it is processing the first wafer on the resource.This could also include situations such as following preventativemaintenance where the chamber in the processing device has been cleanedor perhaps a consumable was replaced in the processing device.

If a processed wafer was the first (or other predetermined) wafer on theresource in accordance with block 103, then the system checks at block105 whether the processing device was idle, greater than some specifiedtime before starting the present process; and if the processing devicewas not significantly idle, the system checks at block 107 whether theprocess was changed or altered. If the process was not changed, ameasurement of the wafer may or may not be-implemented according to theinitial sampling plan at block 116 the wafer-is accordingly measured atblock 120 or not measured at block 118. On the other hand, if theresource was idle for a sufficiently long time, or if the process haschanged, at blocks 109 or 111 respectively, a new measurement is taken.

If the wafer was not the first one on the processing device, then asindicated, at block 113, the system checks whether a significant changewas made to the recipe, such as by the process control algorithm orprocess controller. It is typically desirable to ensure that even if asignificant change was made, the specifications are still satisfied. Achange to the recipe could include time, pressures, flow rates, etc., oreven a completely different recipe. If the recipe was significantlychanged, then at block 115, the system calls for a measurement of thewafer.

The system also checks whether a fault was detected, such as in theprocessing device. Processing devices may be monitored by the factoryautomation system, for example to determine whether there is someproblem with the processing device, either from the automation systemside or from the processing device itself. Also, the processing deviceitself may include the ability to detect a fault. If a fault isdetected, the system could subsequently measure to confirm that thewafer is within specifications. Thus, at block 117, it is determinedwhether a fault was detected. If a fault was detected, at block 123 thesystem measures the wafer. Since it is likely that the wafer has errors,it might be desirable not to use such measurements for feedbackpurposes.

There may be two cases for uses of measurement values. In the firstcase, the system uses the measurement value or stores that measurementvalue for further processing, such as measurements following a resourceidle condition. In the second case, such as following a fault detection,the system may check the wafer or series of wafers for acceptability butdoes not store the value which might skew historical results. In thefirst case, the system is using the historical value for modeling of theprocessing device in order to better predict how the processing devicewill behave, or for other purposes. For example, where a fault is knowto have occurred, the manufacturer will want to find and correct thecause of the fault, often by changing a process component or parameter.Thus, the process data attributed to a wafer that triggered detection ofa fault is not indicative of the “normal” processing in the processsystem. On the other hand, for the fault detection case, the systemmerely ensures that that wafer is a good (e.g., usable) wafer versus abad wafer. Unfortunately, usually following a fault there are severalwafers in a series potentially affected by the fault, and it isdesirable to measure the wafers in the series. Once the wafer(s) aremeasured following a fault, if the wafer(s) are bad, it is desirable tomark the wafer as questionable and discard the measurement value as wellas perhaps the wafer itself.

Similarly, if a wafer is off target despite no change to the recipe, nodetection of a fault, and no other likely cause of error, there islikely to be a series of off-target wafers. Consequently, where a waferwith errors is detected, the next wafer is significantly more likely toalso experience errors. Thus, at block 119, the system checks whetherthe previous wafer was sufficiently far from the target, as determinedby a previous measurement made in accordance with FIG. 1. If so, then atblock 121 the system measures the current wafer as well.

Finally, it may be desirable to measure the wafer according to theinitial sampling plan. Thus, at block 125, the system checks the initialsampling plan to advantageously determine whether the current wafershould be measured according to the initial sampling plan. If not, thenthe system does not measure the wafer. According to one or moreembodiments, a modified sampling plan is used to measure the wafer underappropriate situations, such as after a change of type of chip.

Similarly, if no conditions affecting wafer processing are changed, andif the series of wafers have been on target, one would expect the wafersto continue to be on target. Thus, as indicated at block 127, if themeasurement of the last n wafers were sufficiently on target, there isno need to measure the wafer in this instance or as frequently. In thismanner, the number of measurements can be reduced and processing time ispotentially reduced. On the other hand, if at block 127 the systemdetermines that the last series of n wafers were not on target, at block129 the system measures the current wafer.

Reference is made to FIG. 2, a map of a wafer illustrating measurementregions for the within-wafer dynamic metrology. It is referred to as“within-wafer” since the system may be changing the metrology within thewafer, in distinction to the previously-described wafer-to-wafer dynamicmetrology. (FIG. 3, described in detail below, illustrates an example ofa flow chart for within-wafer dynamic metrology.)

Where the process performed by the processing device on the wafer issymmetric such that the system is affecting portions of the film on thewafer in a symmetric matter, it may be reasonable to measure fewerpoints, perhaps a measurement of only one radii. On the other hand,where there were previous steps performed by the processing device onthe wafer that were asymmetric, information on additional measurementvalues may need to be captured. The number of desirable measurementpoints therefore additionally depends upon the type of process, and uponthe step in the process if applicable.

For instance, given a very uniform process, perhaps only five points onthe wafer need to be measured to provide sufficient precision. On theother hand, given a very non-uniform process or much unresolvedinformation, perhaps twenty-five points should be measured to achieve asufficient level of precision.

Typically the factory automation system, or the software in the factoryautomation system, is programmed to determine which process (orprocesses) or step within a process is being run on which processingdevice. Based on that information, the system can determine whether fewor many points are desired for an adequately precise measurement or setof measurements of the wafer.

Consider, for example, a processing device with multiple chambers orresources independently processing wafers. In this example, the processcontrol algorithm describes four recipe changes. The inventiondetermines which wafers need to be measured (wafer-to-wafer), and anydesired change in number of measurement points due to the dynamic recipechange (within-wafer). This metrology strategy consequently enables adynamic metrology change based on the die map from the MES or otherfactory automation system.

The die map provides a pool of candidate points corresponding to a waferto be measured, and the system can select from among the candidatepoints, the points that correspond most directly to the informationneeded or desired in connection with that wafer. The MES or otherfactory automation system provides information indicating allowable orrelevant possible points that could be measured; from those candidatepoints, one or more embodiments of the present invention contemplatethat the system selects the minimal set of points that would capture thedesired information.

FIGS. 2A and 2B illustrate a plan view and a cross section of an exampleof a typical wafer 201, in this instance having radial regions 1 through5. As shown in FIG. 2A, the illustrated wafer 201 is circular. Chips onthe wafer are usually square and placed across the wafer. At the end ofprocessing, the chips are divided from the wafer. FIG. 2B shows a crosssection of the wafer of FIG. 2A, across section B-B from one edge to thecenter of the wafer. Region 1 extends radially from the center to 40 mm;region 2 extends from 40 mm to 60 mm; region 3 extends from 60 mm to 80mm; region 4 extends from 80 mm to 92 mm; and region 5 extends from 92mm to 95 mm. A wafer could be divided into more or fewer regions. Also,although the regions are illustrated as radial, the same concepts applywhere the regions are neither circular nor radial.

A die map includes a sampling plan that optionally distinguishes amongdifferent regions of the wafer. Such a sampling plan would includeinformation indicating a set of measurement points, associated withregions of the wafer.

The flowchart of FIG. 3 discusses an example of within-wafer metrology,that is, when the system should or should not change the measurementpoints. FIG. 3 thus contrasts to FIG. 1, indicating whether to measure acurrent wafers (wafer-to-wafer dynamic metrology). FIG. 3 defines anexample set of questions to determine whether more points are needed tomeasure a region variation within a given wafer.

Reference is now made to FIG. 3, illustrating an example of thewithin-wafer dynamic metrology, as contemplated by one or moreembodiments of the present invention. At block 301, the wafer ismeasured by the metrology tool utilizing the current sampling plan.Having-measured the wafer, the system analyzes the current wafer todetermine whether there are significant variations that might warrantchanging the sampling plan for the next wafer. The wafers arepotentially changed from run to run. That is, the system performs anaction, and then based upon the results of that action, the systemdetermines whether to utilize the same sampling plan for the next waferor to do something different.

At block 303, it is determined whether there is a variation from thespecification within one or more of the regions on the current wafer. Ifnot, then as indicated by block 305 there is no need to add moresampling points.

At block 307, if there was a variation in a region, it is thendetermined whether the variation was due to an outlier or flier. Anoutlier or flier is a situation in which the measurement point is not anaccurate reflection of the actual value. If there is a speck of dust onthe wafer, for example, this may cause an erroneous thicknessmeasurement; or for instance the actual measured point may besignificantly distant from the correct measurement coordinates,resulting in significantly higher or lower thickness. An outlier orflier can be determined statistically in a number of ways based on howdifferent the measured point is from the expected measurement. It may bedifficult to determine in some cases whether the variation is due to aflier or if there is an actual variation. The data collected could beused to indicate a potentially defective die.

Of course, it should be understood that one or more embodiments of thepresent invention contemplate that any number of other causes forvariations can be detected, and a decision made accordingly as towhether (and how) the sampling plan may be changed.

Referring still to FIG. 3, if the variation from the specification isdue to an outlier or flier, then as indicated by block 309, the samplingplan is not changed. The measurement is not likely to be an accuratereflection of the wafer, and therefore the system should not react tothe measurement.

At block 311, it is determined whether the variation from thespecification is one for which the processing device can possiblycompensate. For example, a processing device may be able to correct forradial variation, but not for a variation that is angular or azimuthal.Thus, at block 313, if the processing device cannot compensate for thevariation in the region, then the sampling plan is not changed. On theother hand, if the processing device can compensate for the variation inthe region, then at block 315 points are added to the region in thesampling plan for the next wafer in order to better characterize theregion. Optionally, the data may be fed back to system controller inorder to change the process in response to this drift condition.

According to one or more embodiments of the inventions, an error in oneor more wafers may initiate some level of error handling and/oralarming. If there is an error that does not result in a change to thesampling plan, such as a non-systematic variation, and even if thesystem cannot compensate, in one or more embodiments of the presentinvention the system might generate an alarm or trigger performance ofother error handling. If the error exhibits the characteristics of asystematic effect, such as wafers out of specification, then an alarmcould be generated. If the error is one wafer that is out ofspecification, according to one or more embodiments of the invention,the system flags that wafer.

The flow chart of FIG. 3 illustrates one potential example ofwithin-wafer metrology. Other types of checks and decisions are alsocontemplated and may be used in combination with, and/or replace, thedetailed checks. For example, an additional check could include whetherthere is a large change in the recipe parameter that could have affecteda specific region; if so, a determination can be made as to whether thechange affected the region to the extent that more information isdesirable; and if so, more metrology points can be added to the samplingplan.

Reference is now made to FIGS. 4A and 4B, illustrating a plan view andsectional view, respectively, of a triangular spiral sampling plan. Thisis one example of a specific sampling plan, showing specific measurementpoints 401 in relation to a wafer 201. Other static sampling plans maybe used. Nevertheless, the illustrated spiral sampling plan is welladapted to capturing both radial change as well as angular change.Consider polar coordinates, where R is the radius and theta isthe-angle; the triangular spiral sampling plan can capture variations inboth the R direction and the theta direction. If the system cancompensate only for variations that are radial, it may be desirable toadd measurement points in the radial direction. Even if a significantangular variation was detected, one might not add any measurement pointsif the variation cannot be corrected anyway due to the manner of holdingand/or spinning the wafer in the processing device.

Still referring to the example sampling plan illustrated in FIGS. 4A and4B, the points 401 are distributed along three splines 403 radiatingfrom the center of the wafer. The points 401 of this example aregenerally distributed in each of eight regions, shown in FIG. 4B. Inthis sampling plan one could potentially add points in a radialdirection. There could be provided more or fewer regions in otherembodiments of the invention. Suppose that in Region 1, which are allpoints radially from approximately 0 mm to 40 mm, there is a largevariation; more measurement points could be added from the die map inorder to better characterize that variation. FIG. 4A indicatesequidistant radii at 24.375 mm from the center, 48.75 mm, 73.125 mm, and97.5 mm for purposes of illustration. It should be noted that thedistance between points 401 along spline 403 advantageously decreasestowards the outer diameter of the wafer, to accommodate the increase inthe surface area in relation to the width of the region.

FIGS. 4A and 4B illustrate only one of many potential sampling plans, inthis instance a particular spiral sampling plan. Other sampling plansare possible. One advantage of the illustrated spiral sampling plan isthat it quantifies not only radial but also angular variation. Anotheradvantage is that it also measures a weighted region, that is itmeasures a selected number of coordinates in approximate proportion tothe wafer surface area that they represent. Closer to the edge of thewafer, measurement points are more dense or closer together, since theradial distance is much further and the area of the region is greater incomparison to the width of the region.

Moreover, the variation on the edge typically will be much higher thanvariation toward the center of the wafer. The variation tends toincrease proportionately further away from the-center. As a result, thedensity of the points to be measured may be advantageously increased asthe points move radially outward.

Furthermore, the present invention optionally optimizes the measuringspeed of the spiral sampling plan. In performance of metrology, ameasurement is faster if performed radially across the wafer. Accordingto the spiral sampling plan contemplated by one or more embodiments ofthe present invention, the wafer may be rotated approximately 120degrees subsequent to a linear measurement, and then the nextmeasurement is taken at the next point positioned radially across thewafer; then the wafer is again rotated approximately 120 degrees for thenext measurement and so forth. The angle of rotation can be varied tocorrespond to the disposition of points as well as to accommodate thecapabilities and/or limitations of the metrology tool. The wafer may bepositioned on a pedestal and rotated and shifted while the metrologytool performs the measurement of the wafer.

Other sampling plans are also contemplated by one or more embodiments ofthe present invention, including a sampling plan with a large number ofpoints, such as forty-nine (illustrated in FIG. 5), or a small number ofpoints, such as five. Other sampling plans with other distributions ofmetrology points, such as distributed in concentric circles or starformations, or other variations may be used in one or more embodiments.

Reference is made to FIG. 6, illustrating a possible computerizedprocess control system which may be used in connection with one or moreembodiments of the present invention. The system includes a standardfactory automation system such as an APC 601. The APC 601 provides forcentral control of, and communication with, one or more standardprocessing devices 603 or resources. In turn, the processing device 603communicates with and controls a standard metrology tool 605, whichmeasures wafers in accordance with the processes described in connectionwith the present invention. Although FIG. 6 illustrates a typicalsystem, other configurations are possible, such as having the metrologydevice(s) 605 communicate with the APC 601, or even omitting the APC 601and having the metrology device 605 pattern the processes describedherein.

Examples of processing devices that may be used in conjunction with theinvention include chemical mechanical planarization (CMP) tools, etchtools, chemical vapor deposition (CVD) tools, lithography tools andothers. It should be noted that the processing device may incorporatethe metrology tool in some configurations.

While this invention has been described in conjunction with the specificembodiments outlined above, many alternatives, modifications andvariations will be apparent to those skilled in the art. Accordingly,the preferred embodiments of the invention as set forth are intended tobe illustrative and not limiting. Various changes may be made withoutdeparting from the spirit and scope of the invention as defined in thefollowing claims.

For example, it would be possible to use any sampling plan with theinvention. A sampling plan may include information in addition to thatmentioned above. Further, a sampling plan may combine information frommultiple sampling plans. As another example, although the abovediscusses a predetermined or static sampling plan, such predetermined orstatic sampling plan includes those sets of coordinate points measuredon the fly such as just prior to wafer processing.

As another example, events or conditions in addition to, in combinationwith, and/or replacing these discussed above, could be checked as partof the wafer-to-wafer metrology determination. For example, a metrologytool, a processing device, or the system itself could indicate a fault.Moreover, it is possible that the reason for the fault could beindicated, and such information could be specifically checked andappropriately handled as well. The system could check for changes to therecipe in several different ways, such as replacement of a recipe, orchange in recipe parameters.

Similarly, other events or conditions could be handled as part of thewithin-wafer determination. For example, there may be one or moreregions of any shape on the wafer. As another example, points could beomitted from the sampling plan in appropriate cases. A further exampleincludes other events mentioned above in connection with wafer-to-waferprocessing.

As another example, the factory automation system may be a generalpurpose computer, or a specially programmed special purpose computer. Itmay also be implemented as a distributed computer system rather than asa single computer; some of the distributed system might include embeddedsystems. Further, the programming may be distributed among processingdevices and metrology tools or other parts of the process controlsystem. Similarly, the processing could be controlled by a softwareprogram on one or more computer systems or processors, or could bepartially or wholly implemented in hardware. Moreover, the factoryautomation system may communicate directly or indirectly with therelevant metrology tool(s), processing devices, and metrology system(s);or the metrology tool(s), processing devices and metrology system(s) maycommunicate directly or indirectly with each other and the factoryautomation system.

1. A computer-implemented method of measuring at least one manufacturingcharacteristic for at least one wafer from a lot of wafers manufacturedby a manufacturing process, comprising: providing informationrepresentative of a set of candidate points to be measured by themanufacturing process on the at least one wafer from the lot of wafers;executing, by a computer system, a plan for performing measurements onthe at least one wafer from the lot of wafers to measure the at leastone manufacturing characteristic, the plan defining at least one of:which of the wafers in the lot of wafers are to be measured and whichcandidate points on the wafers to be measured to make measurements on;detecting one of a plurality of events or a lack of one of the pluralityof events indicating a change in the manufacturing process, the changepertaining to at least one of: detecting a fault in the manufacturingprocess, and detecting a variation in a measurement of the at least onewafer; determining whether to take more or fewer measurements on atleast one subsequent wafer in the lot of wafers to be measured based onthe detected event or lack of the event; and adjusting the plan, in realtime, to increase a spatial density of measurements on at least onesubsequent wafer in the lot of wafers to be measured upon determining totake more measurements, and to decrease the spatial density ofmeasurements on at least one subsequent wafer in the lot of wafers to bemeasured upon determining to take fewer measurements.
 2. The method ofclaim 1, wherein the plan further comprises information representativeof a metrology recipe.
 3. The method of claim 1, wherein the plandefines at least one region on the wafer, each of the candidate pointscorresponding to the at least one region.
 4. The method of claim 1,wherein the adjusting the plan comprises: determining at least oneregion corresponding to the detected change; selecting at least onemeasurement responsive to candidate points corresponding to thedetermined region; assigning the selected at least one measurement as anadditional measurement to be performed or as a measurement to be removedunder the plan; and revising at least one of the measurements, theselected measurement, and the plan.
 5. The method of claim 1, whereinadjusting the plan comprises: determining whether the detected change isof a type that affects a series of wafers; and determining whether tomeasure at least one of the wafers in the series of wafers based on thedetermination of whether the detected change is of a type that affects aseries of wafers.
 6. The method of claim 5, wherein there is provided aplurality of wafers in the lot of wafers, including the at least onewafer, and wherein the plan further comprises: first informationrepresentative of the wafers in the lot of wafers that are available tobe measured; and second information representative of the wafers in thelot of wafers that are to be measured under the plan.
 7. The method ofclaim 1, further comprising discarding information representative ofmeasurement results on the at least one wafer when at least one of: themeasurement results indicate a variation in measurement of the at leastone wafer, and a fault is detected in the manufacturing process.
 8. Themethod of claim 1, wherein the plan comprises: a plurality of splinesradiating from a center of the at least one wafer, the candidate pointsbeing distributed along the splines; and a distribution of the candidatepoints along the splines weighted according to a surface area of the atleast one wafer.
 9. A computer-implemented system of measuring at leastone manufacturing characteristic for at least one wafer from a lot ofwafers manufactured by a manufacturing process, comprising: a memory tostore information representative of a set of candidate points to bemeasured by the manufacturing process on the at least one wafer, andinformation representative of a plan for performing measurements on theat least one wafer to measure the at least one manufacturingcharacteristic, the plan defining at least one of: which of the wafersin the lot of wafers are to be measured and which candidate points onthe wafers to be measured to make measurements on; and a processor,coupled to the memory, programmed to detect one of a plurality of eventsor a lack of one of the plurality of events indicating a change in themanufacturing process, the change pertaining to at least one of:detecting a fault in the manufacturing process, and detecting avariation in a measurement of the at least one wafer; determine whetherto take more or fewer measurements on at least one subsequent wafer inthe lot of wafers to be measured based on the detected event or lack ofthe event; and adjust the plan, in real time, to increase a spatialdensity of measurements on at least one subsequent wafer in the lot ofwafers to be measured upon determining to take more measurements, and todecrease the spatial density of measurements on at least one subsequentwafer in the lot of wafers to be measured upon determining to take fewermeasurements.
 10. The system of claim 9, wherein the manufacturingprocess is an automated semi-conductor manufacturing process, furthercomprising at least one metrology tool for performing measurements onthe semi-conductor wafer, operatively connected to the processor. 11.The system of claim 9, wherein the plan further comprises informationrepresentative of a metrology recipe.
 12. The system of claim 9, whereinto adjust the plan comprises: determining at least one regioncorresponding to the detected change; selecting at least one measurementresponsive to candidate points corresponding to the determined region;assigning the selected at least one measurement as an additionalmeasurement to be performed or as a measurement to be removed under theplan; and revising at least one of the measurements, the selectedmeasurement and the plan.
 13. The system of claim 9, wherein to adjustthe plan comprises: determining whether the detected change is of a typethat affects a series of wafers; determining whether to measure at leastone of the wafers in the series of wafers based on the determination ofwhether the detected change is of a type that affects a series ofwafers.
 14. The system of claim 13, wherein there is provided aplurality of wafers in the lot of wafers, including the at least onewafer, and wherein the plan further comprises: first informationrepresentative of the wafers in the lot of wafers that are available tobe measured; and second information representative of the wafers in thelot of wafers that are to be measured under the plan.
 15. The system ofclaim 9, wherein the memory is further to store informationrepresentative of measurement results on the at least one wafer, exceptwhen at least one of: the measurement results indicate a variation inmeasurement of the at least one wafer, and when a fault is detected inthe manufacturing process.
 16. The system of claim 9, wherein the plancomprises: a plurality of splines radiating from a center of the atleast one wafer, the candidate points being distributed along thesplines; and a distribution of the candidate points along the splines isweighted according to a surface area of the at least one wafer.
 17. Atangible computer readable medium for measuring at least onemanufacturing characteristic for at least one wafer from a lot of wafersmanufactured by a manufacturing process, storing executable instructionswhich when executed on a processing system cause the processing systemto perform a method comprising: providing information representative ofa set of candidate points to be measured by the manufacturing process onthe at least one wafer from the lot of wafers; executing, by themanufacturing process, a plan for performing measurements on the atleast one wafer from the lot of wafers to measure the at least onemanufacturing characteristic, the plan defining at least one of: whichof the wafers in the lot of wafers are to be measured and whichcandidate points on the wafers to be measured to make measurements on;detecting one of a plurality of events or a lack of one of the pluralityof events indicating a change in the manufacturing process, the changepertaining to at least one of: detecting a fault in the manufacturingprocess, and detecting a variation in a measurement of the at least onewafer; determining whether to take more or fewer measurements on atleast one subsequent wafer in the lot of wafers to be measured due tothe detected event or lack of the event; and adjusting the plan, in realtime, to increase a spatial density of measurements on at least onesubsequent wafer in the lot of wafers to be measured upon determining totake more measurements, and to decrease the spatial density ofmeasurements on at least one subsequent wafer in the lot of wafers to bemeasured upon determining to take fewer measurements.
 18. The tangiblecomputer readable medium of claim 17, wherein adjusting the plancomprises: determining at least one region corresponding to the detectedchange; selecting at least one measurement responsive to candidatepoints corresponding to the determined region; assigning the selected atleast one measurement as an additional measurement to be performed or asa measurement to be removed under the plan; and revising at least one ofthe measurements, the selected measurement, and the plan.
 19. Thetangible computer readable medium of claim 17, wherein adjusting theplan comprises: determining whether the detected change may is of a typethat affects a series of wafers; and determining whether to measure atleast one of the wafers in the series of wafers based on thedetermination of whether the detected change is of a type that affects aseries of wafers.
 20. The tangible computer readable medium of claim 17,further comprising instructions for discarding informationrepresentative of measurement results on the at least one wafer when atleast one of: the measurement results indicate a variation inmeasurement of the at least one wafer, and a fault is detected in themanufacturing process.
 21. The tangible computer readable medium ofclaim 17, wherein the plan defines at least one region on the wafer,each of the candidate points corresponding to the at least one region.